LONDON — The first blasts came from deep under the city, muffled by tons of earth and concrete. A 30-minute pause, and another, louder, explosion in a stately square near the British Museum. And then, an eerie quiet.

The people of London had been bracing for such an attack for years. When it came, sirens screamed and helicopters buzzed over a city under attack, but a surreal sense of calm seemed to prevail.

"I'm shocked like everyone else, but everyone knew something like this might happen one day," said Cristina Perez, who was evacuated from the subway after the attacks. "You can't let something like this stop your life. I don't plan to change anything."

But if Londoners proved resilient, they were tested by an assault on a transportation system known to tourists the world over for its colorful Tube map and red double-decker buses, both of which flashed across television screens yesterday.

The No. 30 bus from Hackney to Marble Arch was passing in front of the British Medical Association in leafy Tavistock Square when the bomb blast sent its roof 30 feet into the air.

Afterward, the severed roof of the bus lay on the ground in front of the vehicle, the blue seats of its upper deck now open to the air, and the yellow rails that riders hang onto for support were twisted like broken toothpicks.

Ambulances raced to the scene, and emergency workers swathed the victims, many shivering from shock, in shiny silver blankets.

A woman in a red dress lay on the ground, scattered with debris, as two other commuters tried to stanch the flow of blood.

Makeshift MASH unit

This was the scene of devastation that confronted Dr. Laurence Buckman when he pulled up in front of his office in the British Medical Association building.

Within minutes, Buckman recalled, he and a dozen colleagues set up a makeshift MASH unit in the building's stately courtyard and started treating the victims. They worked for four hours, helping people with multiple fractures, burns, chest and head injuries and, in some cases, missing limbs. Two people died in the courtyard while doctors worked desperately to help them.

"We did what we could," a weary Buckman said yesterday evening. "Did we save lives? I hope a few people had their chances of survival enhanced."

The scenes from the shattered underground trains were murky, captured in ghostly photographs from commuters' cell-phone cameras as they inched their way to safety through smoky tunnels.

Fiona Trueman, 26, from St. Albans, was aboard the Piccadilly Line train that claimed the most victims. "There was a massive bang, the train lights went out and there was a lot of smoke and glass smashing," she recalled. "There was four or five seconds, and then everyone was going 'Oh my God, we can't breathe.' What was running round in my mind was: Am I dreaming? It was surreal. The bomb was in front of the train or on the tracks. I was in the second carriage. There was screaming and coughing with the smoke.

"Screams ... were terrible"

"It was pitch black and people were getting their mobiles," she said. "Everyone was screaming to break the windows. No one was telling us anything, there was no contact from the driver. I don't even know if he made it, to be honest. The screams from the carriage in front of us were terrible."

"I think the driver passed away," said Joseph Aka, 25, another Piccadilly Line passenger. "Because when the train exploded, he didn't say anything after that."

Survivors from the Piccadilly Line estimated they spent half an hour trapped in the blackness, smoke and blood of the subway cars. Some said they wept. Others, strained to make conversation, asking strangers what work they did. The cries of the wounded made it difficult.

"People were helpful, looking after each other, passing around water and mints ... trying to convey messages up and down the train," said Joanne Smith, a passenger on the Piccadilly Line train near Liverpool Street. Passengers finally made it out through the mostly intact rear car. Feeling their way, they walked 15 minutes back to King's Cross Station, fearful all the time of being electrocuted by the tracks, Aka said. The strong helped the injured, walking past mutilated, motionless bodies, he said.

"People were still in their seats, and they were screaming with pain," said Michael Henning, 39, a city employee who was aboard another subway line, the first believed hit. "There were other people that were trapped, and they were just left down there."

Unni Krishnan, a doctor, was walking to the Russell Square subway station when he saw people emerging from the depths covered in blood. He helped tend to the wounded at a nearby hotel.

"They had head injuries; one had eye injuries," he said. "A lot of people had minor injuries, but many were in shock and crying, so we tried to comfort them."

Show of strength

David Bodnariuk, a student at Southwestern University School of Law in Los Angeles who is spending a semester studying international law in London, expressed admiration for the strength of Londoners, who endured the horrific Nazi bombings of World War II and a later campaign by the Irish Republican Army.

"In the midst of this horror was a humanity of monumental proportions," said Bodnariuk, who witnessed the aftermath of the bombing near the Russell Square station. "People running blankets to the scene, paramedics keeping the injured safe and for the most part smiling. ... The London people and emergency operators deserve some kind of credit for what went on today."

British Prime Minister Tony Blair paid tribute to the stoicism and resilience of the people of London and said the terrorists must not be allowed to succeed.

"It is a very sad day for the British people," he said, just one day after the city threw an enormous party to celebrate winning its bid to host the 2012 Olympic Games, "but we will hold true to the British way of life."

Later in the day, with the Tube shut down, the streets were crowded with city workers crammed into jackets and windbreakers beginning the long walk home, or standing in long lines to draw money from cash machines in the usually vain hope of finding a taxi.

Comments in the lines were of the nervously jocular variety: "It's just like those old war films: We'll be singing the 'White Cliffs of Dover' next," said Alistair Moncrieff, an environmental expert.

Monika Kashyap, a railway-company project manager who was walking near Russell Square, consulted a photocopy of a city map to determine the best route to her grandmother's home, where she planned to spend the night. With the subway system and buses shut down, Kashyap said she had no way of returning to her own home in East London.

Kashyap was angry and upset by the bombings but said she believed terrorist attacks on the city were all but inevitable.

"I thought something like this might happen, but it's still a shock. The Underground is an open risk, but I have to use the Tube to get to work whether I like it or not. At the end of the day, if I try to change everything, I won't have a life."